Translation:But it is not warm today.
暖かい and 温かい both mean "warm" and both are pronunced あたたかい. 暖かい is used to mean "surrounding warmth", primarily the temperature, but also a warm and cozy sweater or futon for example (as opposed to one that is physically hot, such as from the dryer or heated by an electric blanket). by contrast, 温かい is used to describe physically warm objects as well as feelings.
Although "but" and "however" are very close in meaning, they are still slightly different. "however" would be しかし.
でも can also mean "however". でも is more like "though that may be the case", whereas しかし is more like "in contrast to the previous statement". Both can be translated as "but" and "however" in different contexts.
https://japanese.stackexchange.com/questions/13631/ - this page has more information on the various "buts" in Japanese.
In another question, 「でも」 is translated as "however" and "but" was rejected. In this question, "however" was rejected. Both "but" and "however" should be accepted.
"hot" is あつい「暑い」
あつい can also mean thick by the way, but the Kanji for あつい (thick) is 厚い.
Can anyone tell me what the hell "But it is not warm today." is supposed to mean? When would you ever use that sentence? Can't it also mean "It is not warm today either."?
I'm wearing my new dress, but it is not warm today.
I will go for a walk in the park, but it is not warm today.
It is very sunny, but it is not warm today.
X despite Y